One proposed technique sets a target vehicle speed equal to a constant vehicle speed, which is kept for a preset time period since the driver's ON operation of a main switch for constant-speed drive control and attains the constant-speed drive of the vehicle at the set target vehicle speed (see, for example, Japanese Patent Laid-Open Gazette No. 2000-6682). This proposed vehicle cancels the constant-speed drive in response to the driver's accelerator-on operation or brake-on operation.